Leave the “Old password” field empty when no password has been set yet.

This password feature however shouldn’t be regarded as a sturdy protection mechanism though and it was never intended as such either. The passwords are easy to crack via various tools such as Atomic Pst Password Recovery and the encryption of the pst-file isn’t based on the password either.

Password protect Exchange mailbox

There is no way to protect the data store of an Exchange account as you can for pst-file. The Exchange data store is an ost-file and doesn’t hold the ability to password protect it.

While you can configure your Exchange account to always prompt for a password, it only applies to the connection to the Exchange server. When you would cancel the password prompt, Outlook will still grant you access to the already cached data on your computer.

The only way to fully password protect your Exchange mailbox would be to set the option to always prompt for the password and to disable Cached Exchange Mode.

Disabling Cached Exchange Mode will however impact your user experience with Outlook as several features of Outlook will only work when Cached Exchange Mode is enabled.

To set the option to always prompt for logon credentials, click on the More Settings… button in while still in your Exchange account settings and select the Security tab.

Setting the option: Always prompt for logon credentials.

Alternatives

As mentioned previously, the protection methods for pst-files and Exchange mailboxes have their limitations. You also can’t password protect data stored in IMAP, Outlook Hotmail Connector and Exchange Active Sync accounts.

Therefore, if you really want to protect your data, consider the following methods or a combination thereof instead.

Password protect Windows.

Lock your computer or log off when you are away (keyboard shortcut: + L).